The field of molecular nonlinear optics (NLO) has attracted increasing attention over the past 20 years, owing to its connection with fundamental issues such as charge transfer and higher order polarizabilities or conjugation, as well as to numerous applications in various fields such as telecommunications, optical data storage and information processing, microfabrication, biological sensors, and so forth. Second-order NLO effects such as second-harmonic generation (SHG) or electro-optic modulation require the design of chromophores that exhibit enhanced quadratic responses. Molecular engineering of one-dimensional (1-D) chromophores has been particularly active, leading to push pull derivatives displaying giant off-resonance first order(â) hyperpolarizabilities. Such chromophores however display an intense absorption band in the visible region due to a strong intramolecular charge transfer (ICT) transition. Novel strategies were thus needed for optimizing the efficiency-transparency tradeoff, especially in the context of the search for effective materials for SHG in the visible. In this perspective, the octupolar route pioneered by Lehn, Zyss, and coworkers offers a wide range of possibilities to warden hanced NLO responses. There has been in recent years a growing number of studies devoted to novel multidimensional and multipolar structures taking advantage of the tensorial nature of hyperpolarizabilities. With 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) as the prototypical structure, a variety of octupolar molecules with a two dimensional(2D) character and a 3-fold rotational symmetry axis have been investigated, such as those derived from trisubstituted and hexasubstituted benzenes, 1,3,5-triazine, triarylamines, hexaazatriphenylene, calixarenes, tricyanomethanideanion, crystal violet and other triarylmethyl cations, cyclopropenylium, and cyanines octupolar molecules of approximated tetrahedral symmetry have also been designed, as well as subphthalocyanines, organometallic complexes, and molecularly bridged nanoparticle arrays.

To achieve improved nonlinearity-transparency tradeoff while taking benefit from the multidimensional tensorial nature of the â tensor, we have prepared and investigated nanoscale propeller-shaped molecules that combine wide transparency in the visible region and enhanced first-order hyperpolarizabilities in connection with a 2-D intramolecular charge transfer taking place between the center and the periphery of the molecules.

The design of tris-donor or tris-acceptor substituted molecules derived from a 1,3,5-triphenylbenzene core aimed at achieving improved transparency as compared to tris-donor/tris-acceptor compounds such as molecules derived from1,3,5-triamino-2,4,6-trinitrobenzene (TATB) or1,3,5-triazine. Phenylene-vinylene oligomers were selected as conjugated rods to ensure effective electronic conjugation between the core and the periphery of the molecules while preserving suitable transparency. The triphenylbenzene core maintains large distance between the conjugated branches, thus preventing strong through space electronic interactions between arms as well as sterical hindrances which could hamper intramolecular charge redistribution (Figure 1).

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